A human mission to Mars is routinely described as the "ultimate objective" for the U.S. space program, but it is too distant in time and too costly to serve as a guide for near-term, manned space activities. Currently, we continue to use and learn from missions to the International Space Station in low Earth orbit.

But what steps should be taken beyond this level? In recent years, without a clearly stated, strategic direction for our civil space program, we've watched it flounder and our space work force depart.

After the Obama administration terminated NASA's Constellation program, which would have returned U.S. astronauts to the moon, the space agency has proposed a human mission to an asteroid — a small body independently orbiting the Sun in the vicinity of Earth — as a substitute to help gain deep-space mission experience.

But because asteroids are not routinely accessible, an appropriate target that would permit easy and safe human access has yet to be found. Unlike the moon, if the launch window to an asteroid is missed, it could be many months until Earth is once again in the correct position for departure.

A workshop of scientists and engineers who studied this problem developed a concept whereby a small asteroid would be captured and brought to near-Earth, or cislunar, space. Next, human crews would be launched directly to this asteroid — now close to Earth, ensuring their relative safety. Once there, they would examine and sample the rock for a few days and then return to Earth.

This is the mission concept being touted as a major step in deep-space missions by human crews. But it adds very little to our knowledge of asteroids and does not adequately prepare crews for future planetary missions.

Unlike asteroids, the moon is a miniature planet of surprising complexity, and accessible at any time. Tasks associated with planetary spaceflight, such as extended stays in partial-gravity and radiation protection, can be studied and mastered on the moon.

Unlike the chemically homogeneous asteroids, the moon's complex geology tells us about its own history and allows us to reconstruct the impact history of the Earth. But most importantly, the moon contains critical material and energy resources that would allow us to create new space-faring capabilities.

Water (hydrogen and oxygen) is the most useful material in space — it supports human life, protects us from radiation, can be used to store energy, and is the most powerful chemical rocket propellant known. The poles of the moon contain huge quantities of water, trapped in the dark craters close to areas in near-permanent sunlight. This gift of proximity would allow people, in concert with robots, to work for extended periods on the moon — harvesting lunar resources to supply and nurture a permanent space transportation system.

Once we've created the capability to begin provisioning ourselves off-planet, we'll have the ability to go to the planets — not simply Mars, but to anywhere in the solar system.

We have a choice. We can create a new, permanent space-faring capability by going to the moon, or we can pursue the asteroid mission, which is reminiscent of earlier flag-and-footprint missions but lacking measurable, long-term value.

We went to the moon in the 1960s to prove that it could be done; we would return to the moon 50 years later to prove that we can use its material and energy resources to create new capabilities and commerce. A cislunar transportation system, developed and powered with lunar resources, will extend our reach into deep space and revolutionize spaceflight.

This effort is not "been there, done that" — it is a wholly new, untried and necessary pioneering enterprise in space.

Paul D. Spudis is a planetary scientist and an advocate for human return to the moon. He recently testified before Congress on a plan for a permanent lunar return.